Fix environment variable reference for mkdocs-material installation

Author: MariusStorhaug

.github/workflows/Docs.yml

@@ -32,7 +32,13 @@ jobs:
 
       - uses: actions/configure-pages@v5
 
-      - name: Install mkdoks-material
+      - name: Install mkdocs-material
+        env:
+          GH_TOKEN: ${{ secrets.MATERIAL_FOR_MKDOCS_INSIDER_PAT }}
+        run: |
+          pip install git+https://$env:GH_TOKEN@github.com/squidfunk/mkdocs-material-insiders.git
+
+      - name: Install plugins
         run: |
           pip install mkdocs-material
           pip install mkdocs-git-authors-plugin